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46 CHAPTER 4: INTERSECTION AND TRAFFIC CHARACTERISTICS BACKGROUND The 2009 MUTCD provides specific guidance for two-way stop-control and all-way stop-control conditions. It identifies the following factors to consider when making intersection control decisions: ï· Vehicular, bicycle, and pedestrian traffic volumes on all approaches. ï· Reported crash experience. ï· Approach speeds. ï· Delay on the minor-road approach. ï· Number and angle of approaches. ï· Sight distance available on each approach. While the 2009 MUTCD provides guidance on type of intersection or traffic characteristics, some states and local agencies use other requirements that are different or more specific. The consideration of a yield, stop, or all-way stop condition may also be influenced by the characteristics of the intersection. FINDINGS Table 15 lists the all-way stop-control criteria for the 2009 MUTCD along with the criteria for a number of states. In addition, it lists the criteria for the ICE process, which is used by several states. Table 16 lists the criteria for traffic control selection at unsignalized intersections, as described in various published studies. Table 17 lists the criteria for several techniques used for selecting pedestrian traffic control devices at an unsignalized crossing. Comparing the criteria listed in Table 15 and Table 16 for stop control and Table 17 for pedestrian traffic control devices demonstrates that a larger variety of criteria are being considered for pedestrian traffic control devices at unsignalized intersections. For example, several criteria are considered with pedestrian traffic control devices but not stop control, some of which could be considered unique for a pedestrian crossing (e.g., crossing distance, distance to the nearest signal or stop, and the presence of a pedestrian generator). Other criteria may also be appropriate for being part of stop- control warrants, such as median presence or the number of lanes on approach. Another way of looking at the various techniques available for making traffic control device selection is to examine the methodology being used within the technique. Table 18 lists existing techniques for selecting a traffic control device. To illustrate the intersection and traffic characteristics used in each of the techniques described in this chapter, a sample unsignalized intersection was identified, and several of the techniques discussed here were applied to select a traffic control device. Table 19 illustrates the intersection and traffic characteristics used in each technique.
47 Table 15. Minimum Data Increments for Variables Used to Evaluate the Need of AWSC at Unsignalized Intersections. Criteria 2009 MUTCD (1) In Addition to MUTCD ICE Process ID (8) IN (9) MD (10) MT (11) PA (12) MN (20) WA (13) WI (18) Area type PI PI PI Benefit-cost ratio PI PI Conflicts, vehicle- pedestrian PA PA Crash history 1 Year 1 Year 3 Years 3 Years 5 Years Delay PA Peak delay for all movements, approaches, and entire intersection PA Each movement Driver expectation PI Left-turn conflicts PA PA LOS PI Each movement Roadway functional class PA PA PA PA PA Sight distance restriction PA PA PA PA Speed 85th Percentile PSL Volume, approach 8 hr ADT ADT ADT 48 hr, peak-hour TMC Peak hour, ADT 12 hr Volume, bicycle PA Volume, pedestrian 8 hr ADT PA PA = per approach, PI = per intersection, PSL = posted speed limit, TMC = turning movement count. Table 16. Minimum Data Increments for Variables Used to Evaluate the Type of Traffic Control at Unsignalized Intersections. Criteria Box, 1995 (52) Nitzel et al., 1988 (51) 2000 HCM (28) Elbermawy, 2004 (55) Han et al., 2008 (56) Jiang et al., 2012 (57) Approach Volume Peak Hour Peak Hour Peak Hour Peak Hour Crash History 2 Years 1 Year Entering Volume Peak Hour ADT Functional Class PA PA Major Left-Turn Volume Peak Hour Peak Hour Peak Hour Posted Speed Limit PA PA = per approach.
48 Table 17. Minimum Data Increments for Variables Used to Evaluate the Need for a Pedestrian Traffic Control Treatment at an Unsignalized Intersection. Source, Treatment NCHRP 562 (22) Tucson (63) Phoenix (64) ADOT (65) Boulder, CO (67) VDOT (66) OR (68) TxDOT (70, 71) Ped. Treat. PHB PHB PHB Ped. Treat. RRFB Ped. Treat. PHB or RRFB Criteria Coordinated signal network Pr Crash history by type 1 Year 1 Year 5 Years Crossing distance PA PA PA Crosswalk marking warrant PA PA Distance to nearest signalized or stop PA PA PA PA Illumination Pr Pr Pr Median Pr Pr Pr Pr Number of lanes on approach PA PA PA On route (school, bike, ped., etc.) Pr Pr Pr Pedestrian generator Pr Pr Pedestrian walking speed Slowest Group Sight distance restrictions PA PA Speed 85 th or PSL PSL PSL PSL PSL PSL PSL Typical compliance with ped. treatments High or Low Unique circumstances PA Volume (bicycle) Peak Hour Peak Hour Volume (pedestrian) 1 hr Peak Hour Peak Hour Peak Hour 1â3 hr 1 hr 1 hr 1 hr Volume (vehicular) 1 hr ADT ADT ADT 1 hr ADT PA = per approach, Pr = presence, PSL = posted speed limit, ADT = average daily traffic.
49 Table 18. Summary of Existing Techniques That May Be of Interest for Phase II. Techniquea Overview O S C F PB Reason to Consider for Further Research 2009 MUTCD (1) Existing Criteria X X X Baseline Box, 1995 (52) Stop/Yield Warrants X X Focus on low-volume, low- speed urban/suburban intersections NCHRP 562 (22) Pedestrian Treatments Warrants X X Criteria consider various pedestrian crossing aspects Tucson, Phoenix, or ADOT (65) Point System for Selecting Pedestrian Treatment X Point system allows for integrating multiple criteria Nitzel et al. 1988 (51) Traffic Control Warrants X X X Considers functional class along with traffic volume, crash history, sight distance, and approach speed Box, 1995 (52) Guidelines for Low-Volume Urban Intersections X X Provides recommendations for lower-volume intersections (total entering volume of 300 veh/hr or less during peak hour) Elbermawy, 2004 (55) Traffic Control Warrants Developed through Simulation Runs of Various Volume Combinations X Based on average control delay and considers turning volume distribution; however, minimal, if any, consideration of pedestrians and bicycles Han et al., 2008 (56) Traffic Control Warrants Developed through Simulation Runs of Various Volume Combinations X Jiang et al., 2012 (57) Traffic Control Warrants (Includes Roundabouts instead of AWSC) Developed through Simulation Runs of Various Volume Combinations X a Column headings: Technique = brief name to describe the technique of interest. Overview = brief overview of the main characteristics of the technique. O = Operations: number of vehicles or users, delay, and LOS. S = Safety: conflicts, number of crashes, and change in crash prediction because of a change in traffic control. C = Combination of operations and safety: criteria that include unique criterion for both operation and safety or criteria based on a formal combination of operations and safety considerations such as benefit-cost ratio. F = Functional class and/or design: such as local or collector versus arterial and roundabouts. PB = Pedestrian and bicycle volume data. Reason to Consider for Additional Review = research teamâs reason that the technique should be considered.
50 Table 19. Intersection and Traffic Characteristics Considered for Each Technique. Criteria Units 20 09 M U TC D A W SC (1 ) 20 09 M U TC D TW SC (1 ) N itz el e t a l., 19 88 (5 1) Bo x, 1 99 5 (5 2) 20 00 H C M (2 8) El be rm aw y, 20 04 (5 5) H an e t a l., 20 08 (5 6) Ji an g et a l., 20 12 (5 7) Major Street Peak-Hour Volume vph X X X X Left-Turn Volume % X X X 8 Highest Hourly Volumes (Vehicular) vph X Average Daily Traffic vpd X Functional Classification - X X X Speed (85th Percentile or Posted) mph X Minor Street Peak-Hour Volume, Both Approaches vph X X X X 8 Highest Hourly Volumes (Combined Vehicular, Pedestrian, and Bicycle) vph X Delay during Highest Hourly Volume sec/veh X Functional Classification - X X Speed (85th Percentile or Posted) mph X Intersection Entering Peak-Hour Volume vph X Entering Daily Volume vpd X Crashes in Past 12 Months - X X X X Crashes in Past 2 Years - X X Crashes in Past 3 Years - X X Legs at the Intersection - X Geometry/Sight Distance - X X Safe Approach Speed mph X X = variable is considered within the technique.
